Method of manufacturing inductance-coils



UNITED STATES PATENT OFFICE.

IVAN L. MILTON, OF EAST ORANGE, NEW JERSEY, ASSIGNOR To WESTERN ELECTRIC COMPANY, INCORPORATED, 015 NEW YORK, N. Y., A CORPORATION OF NEW YORK.

METHOD OF MANUFACTURING INDUCTANCE-COILS.

No Drawing.

To all whom it may concern:

Be it-known that I, IVAN L. MILTON, a citizen of the United States, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Methods of Manufacturing Inductance-Coils, of which the following is a full, clear, concise, and exact description.

This invention relates to inductance coils, such as loading coils, for telephone lines. More particularly, it relates to a method of manufacturing cores for inductance coils whereby more uniform results are obtained in their electrical values.-

For convenience this invention will be described in connection with inductance coils having iron dust cores of the type described in the Elmen Patent Number 1,286,965, of December 10, 1918, on magnet cores. The cores \made in accordance with this patent are composed of finely divided electrolytic iron and insulating material separating the particles of iron, which mixture has been subjected to enormous pressures to give the mixture a specific gravity approximately equal to that for undivided iron. One way in which the coil windings may be placed on a magnet core is described in detail in the Fondiller Patent Number 1,212,755 of J anuary 16, 1917.

It has been found, however, that such iron dust cores as they come from the press are sometimes not suited for immediate use in inductance coils or loading coils for the reason that their electrical values, such as their permeability, are not uniform and stable. It has also been found that some of the cores are magnetized to a certain extent.

The unstable electrical properties of the cores is a particularly undesirable condition, especially when the cores are employed in loading coils, and the like, Where the manufacturing requirements are very rigid. Inaccuraciesin the electrical values of loading coils leadto cross talk and other difliculties when the coils are inserted in signaling lines, such as telephone lines.

According to this invention, the cores preferably prior to placing the windings thereon, are subjected to a process which renders their electrical values, such as their permeability, stable and constant.

Thecores, after coming from the press, are first baked at a suitable temperature un- Specification of Letters Patent.

Patented May 24, 1921.

Application filed March 22, 1920. Serial No. 367,896.

A temperature from 200 to turns of wire around the core and sending an alternating current through the turns, gradually decreasing the current from a maximum value to zero.

After being demagnetized, it is generally found that the demagnetizing process has raised the permeability of the cores somewhat higher than their normal values, a three to live per cent. increase being the average. This increase is temporary in character, the permeability beginning to drop shortly after the completion of the demagnetization. It has been found, however, that the time required for the cores to reach a Steady value is too excessive for commercial manufacture. By baking the cores a second time, the time required to reach this steady state is considerably decreased. The length of and the temperature of this second baking will generally be the same as for the first baking.

Loading coils having demagnetized cores are much more stable than coils having cores slightly magnetized because experience has shown that the change in inductance of a 'coil caused by the application of comparatively small values of direct current, such as Morse telegraph currents, is much smaller in the case of a coil having a demagnetized core.

It is also preferable that the heating and demagnetizing treatments be applied to the core before the windings are placed thereon. One of the advantages gained thereby is the increased ease and certainty with which the coil windings can be adjusted to have a desired ratio of turns between inner and outer windings. This is particularly important in the case of phantom loading coils of the type described for example in the above mentioned Fondiller patent. In such a type of phantom coil, it is necessary to have a strict 11 ratio for some of the winding sections thereon. Any departure from this ratio produces cross talk.

Another advantage in subjecting the coils to the process of this invention prior to the step of winding, is the fact that demagnetized cores may be kept in stock for an appreciable time before being wound, which results in a decrease in the electrical core losses and therefore assists in the manufacture of coils of maximum effective resistance limits, which is the result desired.

It has also been found that it is unnecessary for the core to be cooled prior to demagnetizing the same, since the same beneficial results will be obtained by demagnetizing the core while still hot.

What is claimed is:

1. The process of manufacturing a'magnet core which comprises baking said core, demagnetizing said core and subsequently subjecting said core to a second baking.

2. The process of manufacturing a magnet core which comprises baking saidcore at a temperature of approximately 200 F., demagnetizing said core and subsequently baking said core at a temperature of approximately 200 F.

3. The process of manufacturing an inductance coil having a core which comprises 0 baking said core for several hours at a temperature of approximately 200 F., demagnetizing said core, subjecting said core a second time 'to a temperature of approximately 200 F. for several, hours, and subsequently placing the windings on said core.

' In witness whereof, I hereunto subscribe my name this 17th day of March, A. D. 1920.

IVAN L. MILTON. 

